Enzyme-immunoassay is a rapidly developing research and clinical procedure used for quantitative detection of extremely low levels of biological substances. Synthesis of enzyme-antibody conjugates and enzyme-antigen conjugates is the principal requirement of this method. Present methods generally produce low yields of poorly defined, heterogeneous conjugates. Selective chemical coupling combined with solid-phase affinity binding techniques are proposed to improve conjugate yield and homogeneity. Ribonuclease, beta-galactosidase, peroxidase, and invertase will be bound to affinity columns, activated by chemical coupling agents, and reacted with antibody or antigen. This is proposed to eliminate significant polymerization, incorrect conjugate formation, and enzyme activity and immuno-reactivity losses. Selective washing and elution procedures will allow more effective coupling and simpler purification procedures. Enhanced yields and reproducible homogeneity should greatly improve clinical usefulness.